Changes in the biota of Chany Lake along a salinity gradient

Relationships among salinity and diversity, abundance, biomass of major biological components of Chany Lake (western Siberia, Russia) are examined across a salinity gradient. As salinity increased from 0.8 to 6.4 g l⁻¹, the species richness of aquatic vascular plants decreased from 16 to 2 species, of phytoplankton from 98 to 52 species, and of zooplankton from 61 to 16 species, but changes in species diversity of zoobenthos were negligible. Guest Editor: John M. Melack Saline Waters and their Biota     

Zoobenthic diversity-gradients in the Baltic Sea: Continuous post-glacial succession in a stressed ecosystem

The Baltic Sea, formed after the latest glaciation, is an enclosed, low-saline, non-tidal ecosystem and has steep latitudinal and vertical gradients from sub-arctic conditions in the north to temperate in the south. The sea has undergone rapid changes since the glaciation, and the “ecological age” of the present ecosystem is only about 8000 years. Primary successional processes are still ongoing, and numerous ecological niches (e.g. large-bodied sediment bioturbators) remain available for immigration. The system is species-poor and vulnerable to the threat of exotic invasive species, and to date about 50 zoobenthic species have established populations in the Baltic Sea. The present biota is a mixture of species of different ecological and zoogeographical origin (marine to limnic; northern Arctic marine and limnic, to North Sea and Atlantic marine). The current distribution patterns of zoobenthos are illustrated, using marine, limnic and non-indigenous examples of structure and ecosystem functions. The species richness decreases from over 1600 marine benthic species in the open Skagerrak to about 500 in the western parts of the Baltic Sea, approximately 80 in the southern regions, to less than 20 in the northern regions. On the other hand, limnic species increase diversity in the inner reaches of the Gulf of Finland and the Gulf of Bothnia. Polychaetes, molluscs and echinoderms are dramatically reduced in numbers from the south to the north.     

The effects of ultraviolet radiation on the planktonic community of a shallow, eutrophic estuary: results of mesocosm experiments

This paper describes the results of pelagic mesocosm experiments designed to test the effects of enhanced and reduced ultraviolet radiation (UV) on the planktonic community of a Baltic Sea estuary. The Darss-Zingst estuary consists of a series of brackish lagoons with high concentrations of chlorophyll and dissolved organic matter. The shallow depth of the estuary ensures that organisms in the water are regularly exposed to high levels of photosynthetically active radiation (PAR) and UV. During the summer of 1995 and 1996, four 1-m³ mesocosms were filled with water from the mid-point of the estuary. Each compartment was equipped with a pump to simulate natural rates of wind-induced vertical mixing. The mesocosms were hung in the estuary from a floating raft and were shielded from above by filters to give the spectral treatments PAR only, PAR+UV-A, and PAR+UV-A+UV-B. Enhanced levels of UV-B, i.e. twice that of midday sunlight, were provided in a further treatment by artificial sunlamps. Experiments were conducted for periods of 3–14 days. No significant effects of enhanced or reduced UV-B were observed on chlorophyll a concentrations or photosynthetic performance, although the PAR-only treatment did show higher final chlorophyll concentrations in two of the trials. Phytoplankton pigment composition was measured by in vivo absorption and fluorescence excitation spectra, and was similar in all mesocosm treatments indicating that there were no major differences in functional group composition. Bacterial secondary production rates as measured by thymidine incorporation increased with time in all mesocosms, probably due to enhanced production of phytoplankton exudate. There was evidence for a small depression of secondary production by enhanced UV-B, but only on certain days. Microzooplankton generally increased in all mesocosms to population densities higher than those observed in the estuary, and tended to reach higher final values in the mesocosms exposed to UV. It is concluded that vertical mixing which reduces the residence time of planktonic organisms in the surface layers, and high concentrations of chromophoric, dissolved organic matter, which greatly reduce the penetration of UV-B, combined to protect the planktonic community from UV-B damage. Received in revised form: 5 June 2000 Electronic Publication     

广东典型小型供水水——-契爷石水库浮游生物与富营养化特征分析

于2000年丰、枯水期对契爷石水库的理化因子,浮游生物种类组成,细胞密度等进行了调查研究,并利用有关评价指数对该水库水体的营养水平进行了评价。结果表明,契爷石水库目前已进入富营养化状态,且枯水期较丰水期富营养化程度更为严重,另外,全年有机污染也比较严重。浮游植物丰水期以蓝藻、绿藻为主,枯水期以蓝藻、硅藻为主,该水库属于典型的蓝藻-绿藻-硅藻型水库,且有较高丰度的耐有机污染的裸藻所在。浮游动物以轮虫和桡足类为主,轮虫主要以耐有机、喜富营养的萼花臂尾轮虫（Rrachionus calyciflorus）、前节晶囊轮虫（Asplanchna priodonta）、螺形龟甲轮虫（Keratella cochearis）为主,挠足类主要以无节幼体,桡足幼体为主,成体很少,且主要以剑水蚤为主,喜寡营养的哲水蚤在该水库中没有出现,枝角类种类,数量都很少,多为广温型、嗜暖型种类,其中长额象鼻蚤（Bosmina longirostris）和微型裸腹蚤（Moina micrura）习居于富营养型水体中。     

Prokaryotic diversity in one of the largest hypersaline coastal lagoons in the world

Araruama Lagoon is an environment characterized by high salt concentrations. The low raining and high evaporation rates in this region favored the development of many salty ponds around the lagoon. In order to reveal the microbial composition of this system, we performed a 16S rRNA gene survey. Among archaea, most clones were related to uncultured environmental Euryarchaeota. In lagoon water, we found some clones related to Methanomicrobia and Methanothermococcus groups, while in the saline pond water members related to the genus Haloarcula were detected. Bacterial community was dominated by clones related to Gamma-proteobacteria, Actinobacteria, and Synechococcus in lagoon water, while Salinibacter ruber relatives dominated in saline pond. We also detected the presence of Alpha-proteobacteria, Pseudomonas-like bacteria and Verrucomicrobia. Only representatives of the genus Ralstonia were cosmopolitan, being observed in both systems. The detection of a substantial number of clones related to uncultured archaea and bacteria suggest that the hypersaline waters of Araruama harbor a pool of novel prokaryotic phylotypes, distinct from those observed in other similar systems. We also observed clones related to halophilic genera of cyanobacteria that are specific for each habitat studied. Additionally, two bacterioplankton molecular markers with ecological relevance were analyzed, one is linked to nitrogen fixation (nifH) and the other is linked to carbon fixation by bacterial photosynthesis, the protochlorophyllide genes, revealing a specific genetic distribution in this ecosystem. This is the first study of the biogeography and community structure of microbial assemblages in Brazilian tropical hypersaline environments. This work is directed towards a better understanding of the free-living prokaryotic diversity adapted to life in hypersaline waters.     

Insights into the harmful algal flora in northwestern Mediterranean coastal lagoons revealed by pyrosequencing metabarcodes of the 28S rRNA gene

This study investigated the genetic diversity of phytoplankton communities in six shallow lagoons located on the French coast of the northwestern Mediterranean Sea that represented a trophic gradient ranging from oligotrophic to hypereutrophic. The phytoplankton communities were sampled once a month from spring (May) to the beginning of autumn (September/early October) in 2012 and fractionated by size. Metabarcodes were generated from cDNAs by targeting the D1-D2 region of the 28S rRNA gene and pyrosequenced using Roche 454 technology. Examination of the annotated barcodes revealed harmful algal species not previously documented in these lagoons. Three ichthyotoxic species belonging to Pfiesteriaceae were detected: Luciella masanensis was relatively widespread and abundant in many samples, whereas Pfiesteria piscicida and Stoeckeria changwonensis were found as single barcode sequences. Furthermore, a phylogenetic analysis of barcodes annotated as belonging to Pfiesteriaceae suggested the existence of two previously undescribed clades. The other toxic or potentially harmful dinoflagellates detected through rare barcodes were Dinophysis acuminata, Vulcanodinium rugosum, Alexandrium andersonii and A. ostenfeldii. The two most abundant dinoflagellate taxa were Gymnodinium litoralis and Akashiwo sanguinea with respect to sequence numbers. Four diatom species from the genus Pseudo-nitzschia that potentially produce domoic acid were identified (P. galaxiae, P. delicatissima, P. brasiliana and P. calliantha). These observations are discussed in terms of the literature and monitoring records related to the identified taxa in this Mediterranean area.     

Zooplankton and meiobenthos diversity at the intertidal sandy shores of Jizan and Farasan coastal areas of Red Sea

Distinctive studies were conducted for the identification of meiobenthos and zooplankton at Farasan Islands and Jizan sandy shores. The present work compares the meiobenthos and zooplankton communities at Alhsas sandy shore at Farasan Islands and As-Suways sandy shore at Jizan. Population density, species richness and Shannon-Weiner diversity index were determined for meiobenthos and zooplankton inhabiting both the studied sites. Water criteria; surface water temperature, pH and conductivity were determined for each investigated site. Eleven zooplankton species were defined at Alhsas sandy shore Farasan, nine species were identified at the littoral zone at As-Suways sandy shore, Jizan. Ten meiobenthos species were defined at Alhsas site, Farasan. Only eight meiobenthos species were defined at the intertidal zone of As-Suways site, Jizan. The results were discussed to highlight the effect of water criteria on the spatial distribution of zooplankton and meiobenthos at the investigated sites.     

Fourteen FITC-conjugated lectins as a tool for the recognition and differentiation of some harmful algae in Chinese coastal waters

In order to test the use of lectins as a tool for the differentiation of harmful algal species, 13 species and 23 strains of algae were tested with 14 fluorescein isothiocyanate (FITC)-conjugated lectins, and the results examined using flow cytometry (FCM), epifluorescence microscopy (EFM) and spectrofluorometry (SFM). The lectin probes SBA, WGA, GSL I, DBA and PHA-E could distinguish between morphologically similar Gymnodinium-like species, such as Karenia mikimotoi (GMDH01), Takayama pulchellum (TPXM01) and Gymnodinium sp. (GspXM01), by their different binding activities. With the precise quantitative measurements of binding obtained using SFM and FCM, lectins appeared to be useful in distinguishing different strains of the same species. The results also showed that PHA-E could differentiate Alexandrium tamarense (ATDH04) from other strains of this species, and SJA could distinguish A. tamarense (ATMJ02) from other strains of this species (including ATMJ01). Similarly, PNA could identify A. tamarense (ATDH01, 02, 03); UEA I could recognize A. tamarense (ATCI01-JN, ATCI01); and RCA120 could differentiate Alexandrium sp (AspGX01) from strain AspGX02, which was shown to produce different levels of paralytic shellfish poisoning toxin. Lectin probes could also bind these target cells in mixed algal samples. Positive cells identified by FCM were clearer than negative cells thus, in EFM, both GspXM01 and TPXM01 labeled with a WGA lectin probe could be distinguished from target cells of K. mikimotoi, Prorocentrum donghaiense and P. minimum (PMDH01, PMXM01) in mixed algal samples. FCM, EFM and SFM analysis could clearly distinguish lectin-probe-bound cells from negative cells in culture.     

Photoacoustics: a novel tool for the determination of photosynthetic energy storage efficiency in phytoplankton

Photosynthetic energy storage efficiency controls the development and decline of phytoplankton biomass. All abiotic environmental factors such as light intensity; temperature, nutrient availability and pollutants will exert detectable changes in the photosynthetic energy storage efficiency of phytoplankton, and subsequently affect total biomass and composition of phytoplankton assemblages. Since this efficiency is a sensitive amplifier of ambient conditions, it thereby is an excellent reporter of water quality parameter. We demonstrate the applicability of the novel photoacoustic method in easily and directly estimating the energy storage efficiency of phytoplankton in a drinking water reservoir of different nutrient status. Electronic Supplementary Material Supplementary material is available in the online version of this article at and accessible for authorised users Handling editor: J. Padisak     

Predation-driven dynamics of zooplankton and phytoplankton communities in a whole-lake experiment

Summary 1. Species compositions of zooplankton and phytoplankton were followed in Tuesday Lake before and after experimental manipulation of its fish populations (addition of piscivorous largemouth bass, removal of planktivorous minnows). Plankton dynamics were compared to those of adjacent, unmanipulated Paul Lake, where piscivorous fish have been dominant historically. 2. Indices of similarity for the zooplankton communities in the two lakes in 1984 prior to the manipulation were low; however, following the manipulation in spring, 1985, similarity of the zooplankton in the two lakes rose considerably and remained high throughout 1986. This was the result of an increase in Tuesday Lake of previously rare large-bodied cladocerans (Daphnia pulex, Holopedium gibberum) which were the dominants in Paul Lake, and the disappearance in Tuesday Lake of the dominant small-bodied copepod Tropocyclops prasinus, a minor component of the Paul Lake zooplankton. These observations are consistent with prior observations of the effects of size-selective predation on zooplankton communities. 3. Phytoplankton communities also responded strongly to the manipulation, with similarity indices for the two lakes rising from low levels in 1984 to high levels of similarity in 1985 and 1986, reflecting the decrease of formerly dominant Tuesday Lake taxa which were unimportant in Paul Lake and the appearance or increase in Tuesday Lake of several taxa characteristic of the Paul Lake phytoplankton assemblage. these results clearly show that food web structure can have pronounced effects on community composition at all levels of the food web, and that, just as zooplankton communities are structured by sizeselective predation, phytoplankton communities are structured by herbivory. These observations may provide some insight into factors governing the complex distributions of phytoplankton species among various lakes.A contribution from the University of Notre Dame Environmental Research Center, funded by NSF grants BSR-83-08918 and BSR-86-06271     

Hydrobiological analysis of a peat bog with emphasis on its planktonic diversity and population dynamics in Bumdeling Wildlife Sanctuary, eastern Bhutan

A pioneering limnological investigation was carried out in Bhutan in a small peat bog in the Trashiyangtse district (1950 m above sea level) from February 2000 to January 2002. The sampled pond water had low transparency (55.0–95.0 cm), was typically acidic (pH 5.69–6.58) with soft water (alkalinity, 11.0–36.0 mg/l; total hardness, 10.0–34.0 mg/l), and had low to moderate specific conductivity (17.0–62.0 μS/cm). Further, moderate Na (2.0–6.8 mg/l), K (1.8–13.5 mg/l), sulphate (0.85–2.99 mg/l), and silicate (2.5–15.0 mg/l) concentrations as well as low nutrient levels such as phosphate (0.006–0.170 mg/l) and nitrate (0.003–0.180 mg/l) characterize the water in the peat bog. The recorded net plankton comprised 27 species of phytoplankton and 49 species of zooplankton, with the latter indicating greater homogeneity and breaking down into Rotifera (23 species) > Cladocera (13 species) > Rhizopoda (8 species) > Copepoda (3 species) > Ostracoda = Nematoda (1 species each). On the other hand, the net plankton density ranged between 93 and 692 number/l (n/l) with numerical dominance by phytoplankton (68.5% ± 12%), of which Chlorophyceae were predominant (90 ± 63 n/l). Zooplankton showed moderately high diversity (2.745 ± 0.293) and evenness (0.925 ± 0.049) and exhibited almost equal abundance of four recorded groups, namely Cladocera (20 ± 15 n/l) > Rotifera (15 ± 6 n/l) > Copepoda (14 ± 7 n/l) > Rhizopoda (14 ± 4 n/l). While no significant impact of abiotic factors was recorded on zooplankton density, rainfall alone was the most important factor that influenced net plankton and various groups of phytoplankton. Comments on some comparative limnological attributes are also made with similar as well as different habitats in the nearby Himalayan countries.     

Comparison of productivity and phytoplankton in a warm (Kongsfjorden) and a cold (Hornsund) Spitsbergen fjord in mid-summer 2002

Kongsfjorden and Hornsund are two glacial fjords without sills on the West Spitsbergen coast. Both sites are under the influence of relatively warm Atlantic-derived water, although Hornsund is more influenced by cold water from the Barents Sea. In this study, we compared the impacts of cold Arctic and warmer Atlantic waters on the pelagic ecosystems of Kongsfjorden and Hornsund. Both fjords were strongly influenced by Atlantic-derived waters during summer (2002). Diatoms were the most substantial contributors to phytoplankton biomass, especially in outer basins of both fjords, whereas the second most important contributors were autotrophic dinoflagellates in Kongsfjorden and nanoflagellates in Hornsund. Total phytoplankton biomass was highest in Hornsund. Primary production rates were an order of magnitude lower in Kongsfjorden than in Hornsund, and increased from inner to outer fjord (from 2.47 to 4.48 mg C m⁻² h⁻¹ in Kongsfjorden and from 14.00 to 86.65 mg C m⁻² h⁻¹ in Hornsund). Chlorophyll-a concentration was also substantially lower in Kongsfjorden. Zooplankton was dominated by omnivorous species in Kongsfjorden and herbivorous in Hornsund. Observed differences between the fjords may originate from (1) advection of different waters into the fjords; (2) differences in freshwater runoff and turbidity, and (3) timing of the phytoplankton bloom. Climate warming will likely increase the Atlantic water influence, and result in reduced production of diatoms and increase in flagellates.     

Plankton composition and water quality in a pond of spring origin in Turkey

Phyto/zooplankton composition, chlorophyll a, and some water quality parameters were investigated in a spring-originated pond in Central Anatolia between February 2001 and January 2002. Water temperature, pH, dissolved oxygen, Secchi depth, total and calcium hardness, nitrate-nitrogen, nitrite-nitrogen, ammonia-nitrogen, total phosphorus, and soluble reactive phosphorus levels were analyzed. A total of 49 species belonging to Bacillariophyceae, Chlorophyceae, Cyanophyceae, Cryptophyceae, and Dinophyceae were identified. The highest phytoplankton abundance was found in August, whereas the lowest was determined in January. Phytoplankton abundance increased from February to August and declined in the following months. The Bacillariophyceae were dominant in the phytoplankton community. A total of 21 species of Rotifera, 2 species of Cladocera, and 1 genus of Copepoda were found. The zooplankton community was dominated by Rotifera. The highest abundance of zooplankton was recorded in July and the lowest value in November. The annual mean concentration of chlorophyll a was measured as 1.90 μg l⁻¹. In spite of these eutrophic levels (mean values of total phosphorus and nitrate-nitrogen: 0.069 mg P l⁻¹ and 0.68 mg N l⁻¹), phytoplankton cannot grow satisfactorily because of the short water retention time (0.6 day⁻¹). The shallowness of the pond together with the low phytoplankton biomass and the high concentrations of nutrients are discussed.     

Macroinvertebrate assemblages in 25 high alpine ponds of the Swiss National Park (Cirque of Macun) and relation to environmental variables

High-altitude freshwater ecosystems and their biocoenosis are ideal sentinel systems to detect global change. In particular, pond communities are likely to be highly responsive to climate warming. For this reason, the Swiss National Park has included ponds as part of a long-term monitoring programme of the high-alpine Macun cirque. This cirque covers 3.6 km², has a mean altitude of 2,660 m a.s.l., and includes a hydrographic system composed of a stream network and more than 35 temporary and permanent ponds. The first two steps in the programme were to (i) make an inventory of the macroinvertebrates of the waterbodies in the Macun cirque, and (ii) relate the assemblages to local or regional environmental variables. Sampling was conducted in 25 ponds between 2002 and 2004. The number of taxa characterising the region (Macun cirque) was low, represented by 47 lentic taxa. None of them was endemic to the Alps, although several species were cold stenothermal. Average pond richness was low (11.3 taxa). Assemblages were dominated by Chironomidae (Diptera), and Coleoptera and Oligochaeta were also relatively well represented. Other groups, which are frequent in lowland ponds, had particularly poor species richness (Trichoptera, Heteroptera) or were absent (Gastropoda, Odonata, Ephemeroptera). Macroinvertebrate assemblages (composition, richness) were only weakly influenced by local environmental variables. The main structuring processes were those operating at regional level and, namely, the connectivity between ponds, i.e. the presence of a physical connection (tributary) and/or small geographical distance between ponds. The results suggest that during the long-term monitoring of the Macun ponds (started in 2005), two kinds of change will affect macroinvertebrate assemblages. The first change is related to the natural dynamics, with high local-scale turnover, involving the metapopulations characterising the Macun cirque. The second change is related to global warming, leading to higher local and regional richness through an increase in the number of colonisation events resulting from the upward shift of geographical ranges of species. At the same time the cold stenothermal species from Macun will be subject to extinction. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: R. Céréghino, J. Biggs, B. Oertli & S. Declerck The ecology of European ponds: defining the characteristics of a neglected freshwater habitat     

Seasonal variations in upwelling and in the grazing impact of copepods on phytoplankton off A Coruña (Galicia, NW Spain)

The impact of grazing by copepods on phytoplankton was studied during a seasonal cycle on the Galician shelf off A Coruña (NW Spain). Grazing was estimated by measuring the chlorophyll gut content and the evacuation rates of copepods from three mesh-size classes: 200-500 (small), 500-1000 (medium), and 1000-2000 μm (large). Between February 1996 and June 1997, monthly measurements of water temperature, chlorophyll concentration, primary production rates, and copepod abundance, chlorophyll gut content, and evacuation rates were taken at an 80-m-deep, fixed shelf station. Additionally, the same measurements were collected daily during two bloom events in March and in July 1996. Small copepods were the most abundant through the seasonal cycle. The highest grazing impact, however, was due to the medium and large size classes. Grazing by small copepods exceeded grazing by medium and large copepods only during phytoplankton spring blooms. The impact of copepod grazing (considering all size fractions) was generally low. On average, 2% of the phytoplankton biomass and 6% of the primary production were removed daily by the copepod community. Maximum grazing impact values (9% of the phytoplankton biomass and 39% of the primary production) were found in mid-summer. These results suggest that most of the phytoplankton biomass would escape direct copepod grazing in this upwelling area.     

一种复合微生态制剂对养殖水体中生物因子的影响

[目的]研究海水养殖池塘中投放以芽孢杆菌和假单胞菌为主的一种自主研发的微生态制剂对池塘养殖生物、微生物菌相、浮游生物的影响,以期为建立微生物生态调控技术体系提供参考.[方法]实验期间,每隔15d于试验池塘中泼洒微生态制剂一次,每月末取样测量水体和底泥中异养菌和弧菌密度、浮游生物种类和密度,实验结束时测量养殖生物的生长率和成活率.[结果]该微生态制剂能够显著提高南美白对虾和三疣梭子蟹的存活率和生长速度,试验组南美白对虾的存活率和体重增长率较对照组分别提高了11.3％和1 400％,试验组三疣梭子蟹的存活率和体重增长率较对照组分别提高了1.2％和37.5％;微生态制剂能够显著提高海水池塘的异养菌总数,从而抑制致病性弧菌的数量,试验组池水和底泥的异养菌平均密度在整个养殖期较对照组提高了58.5％和51.3％,而试验组水体中致病菌——弧菌的数量在整个养殖期较对照组降低了39.7％;微生态制剂使绿藻门和硅藻门的藻类密度明显增加,对蓝藻和甲藻的生长有抑制作用.[结论]该微生态制剂能够有效地改善养殖池塘中生物群落结构,提高某些养殖品种的生长速度.     

GEM: a generic ecological model for estuaries and coastal waters

The set-up, application and validation of a generic ecological model (GEM) for estuaries and coastal waters is presented. This model is a comprehensive ecological model of the bottom of the foodweb, consisting of a set of modules, representing specific water quality processes and primary production that can be combined with any transport model to create a dedicated model for a specific ecosystem. GEM links different physical, chemical and ecological model components into one generic and flexible modelling tool that allows for variable sized, curvilinear grids to accomodate both the requirements for local accuracy while maintaining a relatively short model run-time. The GEM model describes the behaviour of nutrients, organic matter and primary producers in estuaries and coastal waters, incorporating dynamic process modules for dissolved oxygen, nutrients and phytoplankton. GEM integrates the best aspects of existing Dutch estuarine models that were mostly dedicated to only one type of ecosystem, geographic area or subset of processes. Particular strengths of GEM include its generic applicability and the integration and interaction of biological, chemical and physical processes into one predictive tool. The model offers flexibility in choosing which processes to include, and the ability to integrate results from different processes modelled simultaneously with different temporal resolutions. The generic applicability of the model is illustrated using a number of representative examples from case studies in which the GEM model was successfully applied. Validation of these examples was carried out using the ‘cost function’ to compare model results with field observations. The validation results demonstrated consistent accuracy of the GEM model for various key parameters in both spatial dimensions (horizontally and vertically) as well as temporal dimensions (seasonally and across years) for a variety of water systems without the need for major reparameterisation.

Seasonal and diurnal changes of chlorophyll in a tropical fresh water impoundment

The phytoplankton biomass was estimated in terms of chlorophyll in Sathiar reservoir. The chlorophyll values were high during the low water phase in the reservoir which was also the period of summer. Following the rains and increase in water depth phytoplankton biomass decreases on account of (a) dilution, (b) loss from the reservoir through the outlets and (c) settling to the bottom along with silt. The diel variations of chlorophyll showed that the peak value was reached mostly at 12 noon due to the migration of phytoplankton to the surface.     

Index of size distribution (ISD): a method of quality assessment for coastal lagoons

A new index was developed as a tool for quantifying the degree of disturbance in lagoons in order to meet the objective of Ecological Quality Status (EcoQ), using the zoobenthos quality element. The Index of Size distribution (ISD) is proposed to assess the ecological quality status of coastal lagoons. It represents the skewness of the distribution of individuals of a benthic community in geometric size (biomass) classes. The ISD was applied in three coastal lagoons with different levels of disturbance and classified them as of good, moderate and poor ecological quality. A scheme for the classification of EcoQ in lagoonal systems is presented. The index showed a strong relationship with the percentage of organic carbon in the sediment, as well as with the dissolved oxygen concentrations. ISD having the advantage of good discriminating power and not demanding high taxonomic resolution, could be a simple and promising tool to be further applied and tested in Mediterranean lagoons.